A computer program may include a number of different transactions that are executed by a number of different computing systems. In certain circumstances, at least some of the transactions may need to be executed in a particular order. For instance, some transactions may need to be executed before other transactions for the program to provide a correct result. One method of controlling the order in which transactions are executed is to only issue transactions in the order in which they need to be executed. Another method of controlling the order in which transactions are executed is to use barrier commands. A barrier command can be used to hold a computing system to a particular state until specified conditions are met. For example, a barrier command can prevent a computing system from executing certain transactions until other transactions have been executed.